1. Field of the Invention
Aspects of the present invention relate to techniques for use in a wireless communication system. More particularly, aspects of the present invention relate to techniques for supporting emergency communications in a wireless communication system.
2. Description of the Related Art
Wireless communication networks provide various communication services such as a voice service, a video service, a packet data service, a messaging service, a broadcast service, etc. These wireless communication networks may be multiple-access networks capable of supporting communications for multiple users by sharing the available network resources. Examples of such multiple-access networks include a Code Division Multiple Access (CDMA) network, a Time Division Multiple Access (TDMA) network, a Frequency Division Multiple Access (FDMA) network, an Orthogonal FDMA (OFDMA) network, and a Single-Carrier FDMA (SC-FDMA) network.
Services provided by the wireless communication networks may include the ability to make and receive calls including voice calls and emergency voice calls and the ability to send and receive data including data transmitted using the Internet Protocol (IP). To make and receive voice calls with efficient usage of network resources (e.g. wireless spectrum and wireline signaling and transmission lines), networks and terminals may support Voice over IP (VoIP) for normal calls and for emergency calls. In a case of emergency VoIP calls, networks that support radio access according to 3rd Generation Partnership Project (3GPP) and 3GPP2 standards (which includes networks that employ Global System for Mobile communications (GSM), Wideband CDMA (WCDMA), cdma2000 Evolution-Data Optimized (EvDO) and Long Term Evolution (LTE)) may employ a solution in which support is provided using an IP Multimedia Subsystem (IMS). When the IMS is employed, the VoIP emergency call is sometimes referred to as an IMS Emergency Call as call control and call signaling is supported by the IMS in the network that is serving the user's terminal. In this context, a terminal may also be known as a mobile station or User Equipment (UE).
A UE may be invoked by a user to place a VoIP emergency call with a wireless communication network. The UE may go through several phases, such as registration and call establishment, in order to originate the VoIP emergency call. The UE may register with the wireless network so that the UE can be authenticated to the wireless communication network and the wireless communication network may obtain pertinent information such as verified identification information and a verified call back number. The UE may then perform call establishment in order to connect the call to an appropriate entity, e.g., a Public Safety Answering Point (PSAP), which can service the emergency call.
However, not all emergency calls are supported by all wireless communication networks. For example, in 3GPP LTE systems, the emergency calls are not supported in release 8, but emergency calls should be supported in release 9. However, a network version is not broadcast to the UE in either release 8 or release 9. Thus, if a release 9 UE wants to perform an emergency call in a given cell, the UE cannot be sure that an emergency call can be established in the cell, since it is not sure of the network version. In such a case, it is difficult for the UE to determine if it is possible to make an emergency call in the current cell. Therefore a technique should be devised that allows the UE to determine if emergency calls are possible in the given cell regardless of the network version.
Therefore, a need exists for techniques for supporting emergency communications in wireless communication system.